The present invention relates to a memory selection device for a brake control system.
Modern brake control systems, such as anti-skid control systems and automatic brake control systems for example, can be implemented as programmed microprocessors. Microprocessors bring significant advantages in terms of reliability, flexibility, and long term accuracy over the analog circuits used in the past.
However, because a microprocessor operates sequentially rather than in parallel, steps must be taken to maintain the signal processing time of the microprocessor within acceptable limits. Minimization of processing time is particularly critical in anti-skid control systems, where quick relaxation of braking action may be essential in preventing the development of a skid.
One approach to microprocessor based, multiple wheel, brake control systems is to use a common control program for each of the wheels in order to minimize memory requirements. Where appropriate, constants which are common to all wheels, such as thresholds, gains and the like, can be made part of the common control program. However, wheel specific variables such as measured wheel speed, as well as other dynamic variables which must be stored over time, cannot be made part of the common control program. This is because the set of variables corresponding to the particular wheel being controlled must be used. Typically, the appropriate set of wheel specific variables will change with each execution of the common control program as the microprocessor processes in sequence the various wheels being controlled.
A conventional approach to this problem is simply to indirectly address the wheel specific variables, using a calculated address that corresponds to the appropriate set of variables. This approach may, however, excessively increase the processing time, because indirect addressing by calculated address requires a significantly greater execution time than does direct addressing. In addition, indirect addressing modes require increased memory for program storage for many microprocessors.